The invention relates to plasma image display devices in general, and more particularly to an improved plasma image display device.
A plasma display device comprising a gas-tight envelope, the interior of which is divided into a gas discharge space and an electron acceleration space which contains an image screen with fluorescent phosphors, and auxiliary electrodes for line scanning and further auxiliary electrodes, arranged perpendicularly thereto, for brightness control is known.
This device contains a matrix of gas discharge cells, having associated anodes for controlling the rows and control electrodes for controlling the brightness of the columns. In the interior of the gas-tight envelope of this image display device, an auxiliary gas discharge path between a cathode and the auxiliary anodes is provided along with an electron accelerating path between the control electrodes and an anode. A hole matrix consisting of a plate of insulating material divides the common interior of the envelope into an auxiliary discharge space of relatively great length for the gas discharge current, operating at low voltage, and a second space with a short travel distance and high field strength for accelerating the electrons. The insulating hole matrix serves as the carrier for the auxiliary anodes associated with the cells of the matrix. The control electrodes for the brightness control of the columns may be arranged on the opposite flat side of the matrix. The electrons which are generated by the auxiliary glow discharge in a controlled row by row manner and are moved toward the auxiliary electrode, are controlled element by element in the following discharge path of high field strength by the correspondingly subdivided control electrode, accelerated toward the anode and imaged on the latter's fluorescent screen. The anode is preferably designed as a continuous (non-mosaic) screen electrode. On it, the electrons are imaged as defined picture elements. If a row of the auxiliary electrodes is energized, the discharge glows uniformly along the entire electrode, while the negative glow covers a region, the area of which is determined by the well known dependence of the current density at the cathode and by the gas pressure.
In this embodiment of an image display device, the glow discharge space is therefore not separated from the acceleration space. For this reason, the choice of the kind of gas, the gas pressure and the cathode material must be made such, in the known image display device, that, on the one hand, an optimum glow discharge with, in particular, maximum current density is made possible in the glow discharge space, but that, on the other hand, the firing of an independent discharge, which is also called a dielectric breakdown and which prevents an electron beam from being generated, is precluded in the acceleration space. The magnitude of the accelerating voltage is therefore fixed in the known image display device by the choice and the pressure of the gas charge to a predetermined maximum value, which also determines the luminous density of the phosphor image screen.